This invention relates to use of a phosphorescent dye to emit light and create a mark on photographic film during autography.
Autography is a process utilized in scientific research and clinical diagnostic procedures where the distribution of a radioactive or a photon-emitting substance, e.g., a radioactive isotope-containing compound or chemiluminescent material, in a "labelled" or "tagged" object, surface, or material (e.g., a flat dried electrophoretic slab gel) is visualized. Typically, this visualization is by placing a sheet of photographic film (e.g., X-ray film) adjacent to, preferably in contact with, the object for a period of time and then developing the film to form an autogram. The pattern of ionizing radioactivity or photon-emitter in the object generates a corresponding dark pattern against a light or transparent background on the film. When the labelled-emitter substance is a radioactive compound the process is called autoradiography and the developed film an autoradiogram.
It is useful to identify an autogram by placing some form of reference marking on the object which will, in turn, cause a recognizable pattern on the film. Such a pattern assures that the original object and the developed film can be identified as a pair, and that corresponding locations on the object and film can be determined.
Two methods of marking autoradiograms have been and are currently utilized in laboratories. One method involves marking a radioactively tagged object, in an area lacking radioactivity, with dark radioactive ink. The other method involves marking radioactive or non-radioactive objects in untagged areas with phosphorescent (luminescent) ink. Both methods are described by Litt et al., U.S. Pat. No. 4,510,392. Litt et al. describe the problems and disadvantages associated with use of a radioactive ink marking means such as a pen or dotting devices as follows:
"1. Leakage can lead to general, although low level contamination. PA0 2. Multiple pens must be prepared as it is necessary to approximate the amount of radioactivity in the substrate. In addition, it is necessary in many cases to match the particular radionuclide under study. PA0 3. The intensity of marking actually attained on the film is dependent not only upon time of exposure and radionuclide energy, but also is affected by the plastic overlays commonly used and, in some special cases, temperature. PA0 4. There is significant potential for `abuse` in that a convenient pen will potentially migrate from the laboratory."
The phosphorescent ink marking method of Litt et al., is used in a commercially available pen manufactured and sold by DuPont NEN Products. The pen dispenses a thick ink carrying, in suspension, a phosphor formed of hexagonal Wurtzite crystals of zinc sulfide doped with various trace metals. After the ink markings are made and have dried on the object to be autographed, the object is exposed to actinic or ordinary room light to activate the phosphor. Shortly thereafter the object is placed in contact with X-ray film. Phosphorescence generated from the dried ink is almost exhausted within thirty minutes. Therefore an autographic film exposure carried out for thirty minutes or more will, upon photographic development, exhibit more or less constant and predictable darkened markings corresponding to the phosphorescent ink markings.
In the field of medical X-ray diagnosis, an apparatus described by Byler, U.S. Pat. No. 3,631,243 employs a short afterglow phosphorescent marking unit for X-ray film. The phosphorescent surface of the unit is first overlaid with identifying indicia (e.g., the patient's name), then exposed to room light and immediately inserted into and, 4-5 seconds later, withdrawn from a specialized housing containing the X-ray film. The short afterglow phosphorescent composition (such as a variety of copper-activated zinc sulfide) on the marking unit is selected so that it is energizable to emit visible light which decays rapidly in brightness from a maximum immediately after energization. The rapid completion of phosphorescent light emission from the unit generates a constant and predictable film darkening over the phosphorescent marking unit after a film exposure of several seconds. The marking unit of Byler must be inserted quickly, e.g., in about 0.4 seconds, and held against the film for only about 4 or 5 seconds, after which "the diminishing afterglow from the phosphor does not add significantly to the cumulative light output . . .". The rapid decay necessitates a rapidly insertable unit and various hardware design features including a "guiding means constructed to guide the unit so that when the unit is inserted into the film-loaded housing through said aperture the film is immediately and directly exposed to any emitted light . . ."